Historically, complexes containing isonitrile ligands have been limited to those containing the few commercially available isonitriles like t-BuNC, PhNC, or the readily synthesized and purified isonitriles like MeNC, EtPhNC, MeOPhNC, MePhNC wherein tBu=tertiary butyl, Ph=phenyl, Et=ethyl, and Me=methyl. For a review see: Bonati, F.; Minghetti, G. Inorg. Chim. Acta 1974, 9, 95-112. Only recently have complexes containing more `exotic` isonitriles been studied (Winzenburg, M. L.; Kargol, J. A.; Angelici, R. J. J. Organomet. Chem. 1983, 249, 415-428).
Salts of the type [L.sub.4 M][M'X.sub.4 ] are known as double-complex salts, i.e. the salt is composed of two metal-containing complex ions. Salts where L is often an amine or isonitrile, X is a halide or cyanide, and both M and M' are platinum have been known for many years. For a recent review of metal isocyanide complexes see: Singleton, E., Oosthuizen, H. E. Adv. Organomet. Chem. 1983, 22, 209-238. Both the cation and anion comprising these complexes have square-planar geometries and often assume structures in which the ions form mixed stacks; the resulting metal-metal interactions cause these solids to be intensely colored despite the fact that the component ions absorb below 350 nanometers(nm) (Bonati, F., Minghetti, G., J. Organomet. Chem. 1970, 24, 251; Isci and Mason, Inorg. Chem. 1975, 14, 913; Mason, W. R., Gray, H. B.. J. Am. Chem. Soc. 1968, 90, 5721). A study of the optical properties of these complexes is reported by Isci and Mason, (Inorg. Chem. 1974, 13, 1175-1180).
Simple salts having cations of the type [(RNC).sub.4 M].sup.n+ where M includes radioactive isotopes of Rh(n=1) and Ni, Pd, or Pt(n=2) are described in U.S. Pat. No. 4,452,774 for use as diagnostic agents for labeling living cells. U.S. Pat. No. 4,271,033 describes binucleating biisocyanide complexes of Rh, Pt, Pd, Ni useful as catalysts. Isonitrile or isocyanide complexes of copper, described in U.S. Pat. No. 3,197,493, are useful as intermediates in the preparation of isonitriles.
U.S. Pat. No. 4,130,432 claims alkyl tin tetracyanometallates as biocides. Double salts of tetracyanoaurate useful for plating gold alloys are described in U.S. Pat. No. 3,458,542.
Use of transition metals in sensors is known in the art; transition metal complexes used have predominantly been phthalocyanine or porphyrin derivatives as seen, for example, in U.S. Pat. No. 4,381,922 and U.S. Pat. No. 4,350,660.
A patent on organometallics dealing with sensors is U.S. Pat. No. 4,152,118 which claims a phosphine copper complex which functions as a sulfur dioxide indicator. U.S. Pat. No. 4,442,297 describes manganese complexes which coordinate hydrogen, carbon monoxide, oxygen, sulfur dioxide, and alkenes and can be used as indicators or gas separators.
Methods have been devised to chemically trap and analyze vapors as taught in U.S. Pat. No. 4,102,201; however, such methods do not allow for immediate (real time) indication of organic vapors.
Sensing of gases using optical waveguide gas sensors was first reported in 1975 by Hardy, David, Kapany, and Unterleitner, (Nature 1975, 257, 666-667). State of the art optical waveguide sensors often utilize chemically reactive dyes which, unfortunately, often have limited shelf life, may undergo irreversible chemical changes and are chemically specific as described by Giuliani, Wohltjen, and Jarvis, (Optics Letters 1983, 8, 54-56, and references cited therein).